In the U.S., the main body developing the design standards of kilns, furnaces and ovens is the National Fire Protection Association (NFPA), through NFPA 86 Standard for Ovens and Furnaces. But the ceramic industry has misconceptions about NFPA 86, and no wonder. In essence, as an advisory publication, NFPA 86 “has no power…nor does it undertake to police or enforce compliance with the contents of NFPA standards.”1 On the other hand, NFPA 86 has well over a hundred pages of definitions and standards encompassing a wide range of design standards to be applied to Class A, B, C, and D ovens, dryers and furnaces, and thermal oxidizers, dictating that key components be listed, etc. These standards address a wide range of design parameters, including structural details, combustion safeguards, and electrical design.
If NFPA does not police or enforce compliance, who does? The short answer is: “the authority having jurisdiction (AHJ).”1 The AHJ could be a number of entities, including direct adaptation by the Occupational Safety and Health Administration (OSHA); your industrial risk insurer; your local fire marshal; or your state, county, city, etc. Occasionally, kiln users have virtually no idea who will regulate or inspect a finished system. Sometimes systems are inspected, and sometimes they are not. It is a very odd system because it is not universally required or enforced.
What is NFPA 86?
The goal of the NFPA 86 standards is clear—to reduce the loss potential in terms of life, property and production. The technical committee is composed of a variety of experts in insurance, safety, combustion equipment specialists, and end users, and they adopt standards by consensus. One of their most important criteria is case history analysis of disasters. Forensic analysis provides critical information—after all, if the cause of the incident is documented properly, then the design and equipment parameters can be revised to eliminate the cause. NFPA 86 technical committee members represent a cross-section of interested parties, and their judgment of required design standards should represent the optimum solution in terms of safety combined with cost.
What about modifications of older systems? Hundreds of systems are in use that do not meet current standards because they have been grandfathered. NFPA’s position here is somewhat contradictory. The standards (2015) “reflect a consensus of what is necessary to provide an acceptable degree of protection…”1 yet at the same time, they state that “unless otherwise specified, the provisions of this standard shall not apply”1 to equipment that existed before the effective date of the standard. They do recommend that if the unit is modified, it should be brought up to current standards. Draw your own conclusions or seek assistance from your AHJ.
Adherence to NFPA 86 represents good business sense and ethical design. The extra costs are justified to minimize risk for our customers and their employees. Taking shortcuts to reduce cost is unethical, and in today’s litigious environment, it is also foolish. What’s at stake here? Following are a few examples (see Figures 1-3):
- An operator defeated the burner lighting interlocks on a tunnel kiln, resulting in well over $1 million in damages and lost business.
- Apparent failed safety systems in an insulator product periodic kiln caused a natural gas explosion, causing extreme damage.
- A kiln exploded at a facility manufacturing filtration media. In addition to plant and kiln damages, two people were hospitalized and others were injured.
Let’s broadly consider the standards themselves, specifically as related to industrial ceramic kilns (which can be Class A, B or C systems). The thrust of all of the standards involve the minimization of explosion or fire hazard risks, combined with additional safeguards in the event that an explosion occurs. The concentration of effort is to avoid the case where the explosive limits of fuel are allowed to exist, whether the flammable material comes from the fuel being used or if it emanates from the product being fired. Major emphasis is placed on the pre-startup sequence (i.e., what has to be done prior to lighting the burners in the system) because most incidents occur when a system is started. While the standards are voluminous, they can be distilled into four broad areas:
- Location and construction
- Heating systems
- Electrical management
- Commissioning, operations, maintenance, inspection and testing
Location and construction are straightforward; the system should be located in an area where obvious hazards do not exist. The structural requirements include either the use of explosion relief panels (designed to relieve internal pressure in case of an explosion), or construction of the system shall be built out of 3/16-in. steel plate in order to contain the explosion. Figure 4 shows a portion of kiln wall built of expanded metal walls (and no explosion relief panels); this does not meet NFPA structural standards. Quite often, systems like these require other system upgrades, but the inadequate construction precludes retrofit without expensive modification of the structure to meet the 3/16-in. structural plating standard.
Heating system requirement standards cover an extremely broad range of design parameters—defining the location of components combined with their suitability for use. The recognition that fuel isolation valves do fail leads to redundancy combined with proof that the valves actually close when required. Even new electric solenoid valves do not positively stop fuel flow; manufacturers of these valves provide a specification of closed leak rate. Again, since the majority of incidents happen at the initial light-off of systems, significant emphasis is placed on fuel isolation, purging the internal kiln space prior to lighting to ensure that no significant combustibles are present pre-ignition.
Many products release volatile fuels during the firing process. Indeed, today’s ceramic forming techniques increasingly incorporate a range of organic plasticizers; these materials can obviously create explosive conditions during the heating process. Monitoring the internal kiln and oven space for flammability is thus imperative in these cases. The consideration of what happens during a power failure is also critical when heat processing products with these characteristics; when ventilation ceases (e.g., power fails), the continued volatile release can create a hazardous condition.
The mitigation of these special conditions is imperative and can be handled in several ways. Electrical controls must manage all of the protective devices and do so in a logical way. Older hard-wired systems are gradually giving way to tamper-proof safety programmable logic controllers (PLCs). Many times, misguided maintenance people have bypassed critical safety devices, purge timers, etc., at high risk. Although a safety PLC might have an initial cost that is 25% higher than hard-wired systems, the advantages of security, simplified troubleshooting, reliability, and diagnostics make this component almost essential for long-time operation.
Lastly, each facility must recognize the inherent risk in the operation of ovens and furnaces, regardless of code application and rigorous design. The lifecycle of most systems is measured in decades; proper maintenance, testing and inspection should be a part of standard procedure. Replacement of key devices before the end of their lifecycle should be done with discipline, and the training of all operators and maintenance personnel should be a continuous process.
In summary, the goal of these codes is the mitigation of risk. Overlooking the NFPA 86 standards due to cost considerations or lack of knowledge is no excuse for allowing excessive risks in your facility. Understanding the philosophy of code development—and realizing how potentially damaging a single incident can be—should be utmost in the minds of designers and end users. Systems designed today can operate for dozens of years. The consistent review of code updates, qualified testing and inspection of operation of safety devices, and training of operations and maintenance personnel are simply good business.
For additional information, contact the author at (412) 788-7100 or firstname.lastname@example.org, or visit www.swindelldressler.com. The National Fire Protection Association can be found online at www.nfpa.org.
1. NFPA 86 Standard for Ovens and Furnaces, 2015 edition.
This article was originally posted on www.ceramicindustry.com.